rename kk delete image_registry to kk delete registry

[redscholar]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Supplement: #2634

To match with kk init registry, change kk delete image_registry to kk delete registry.

Which issue(s) this PR fixes:

Fixes #

Special notes for reviewers:

Does this PR introduced a user-facing change?

none

Additional documentation, usage docs, etc.:

[kubesphere-prow]

This PR has multiple commits, and the default merge method is: squash.
You can request commits to be merged using the label: tide/merge-method-merge

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[kubesphere-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: redscholar

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [redscholar]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[sonarqubecloud]

Quality Gate failed

Failed conditions
6.4% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[pixiake]

/lgtm

[kubesphere-prow]

LGTM label has been added.

Git tree hash: be0548643d2947091430ac599becae90394c78fb